1. Field of the Invention
The present invention relates to a clutch cover assembly, and in particularly to a clutch cover assembly having a truncated conical spring between a diaphragm spring and a clutch cover.
2. Description of the Related Art
In general, a clutch cover assembly is composed of a clutch cover that is fixed to a flywheel, a pressure plate for clamping a frictional member of a clutch disk to a flywheel, and an elastic member for pressing the pressure plate toward the flywheel.
Usually, a diaphragm spring is used as the above-described elastic member. The diaphragm spring is composed of an outer circumferential disk-like elastic member that extends annularly, and a plurality of lever portions that extend radially inwardly from an inner circumferential edge of the disk-like elastic member. Generally, there are two functions associated with the diaphragm spring, the first is to bias movement of the pressure plate with respect the flywheel and the second function is to provide a lever for counteracting the biasing force acting on the pressure plate.
Stated more specifically, in a so-called push type clutch, the radially inward portion of the disk-like elastic member of the diaphragm spring is supported by the clutch cover through a support mechanism. The radially outward portion of the disk-like elastic member thereof pushes the pressure plate toward the flywheel. When end portions, in the radially inward direction, of the lever portions are depressed by a release bearing, the pressure from the diaphragm spring to the pressure plate is released to thereby disengage the clutch.
The force used to counteract or release the biasing force of the diaphragm spring is generally referred to as a release load and the movement of the diaphragm spring as the release load is being applied is referred to as the release stroke. The diaphragm spring typically has spring characteristics such that the required release load decreases as the release stroke progresses (as the level of deformation of the diaphragm spring progresses).
Accordingly, if the diaphragm spring is the only elastic member used in the clutch for the above-mentioned functions, it is possible that undesirable clutch operation feeling may be experience by the vehicle operator. To cope with this, in some clutches, a conical spring is disposed between the clutch cover and the diaphragm spring.
The conical spring extends along the disk-like elastic member of the diaphragm spring with its outer circumferential edge seated on a back surface (surface opposite to the pressure plate) of the diaphragm spring and with its inner circumferential edge supported by the clutch cover. Also, the spring characteristics of the conical spring are set so that the force applied from the conical spring to the pressure plate increases as the release stroke of diaphragm spring increases.
Accordingly, the composite loads of the two springs are applied to the pressure plate. The release load applied to the pressure plate substantially in proportion with the release stroke due to the combination of the force of the diaphragm spring and the conical spring. As a result, a desired clutch operation feeling may be obtained.
However, in the conventional structure, to prevent the rotation of the conical spring and to position it, a support plate or ring is mounted on an inner surface of the clutch cover. The support plate is fixed to studs of the support mechanism fixed to the clutch cover and has cutaway portions with which projections or the like of the conical spring engage.
If such a support plate is provided, the structure becomes more complicated from the resulting increase in the number of the mechanical parts. Also, the length of the stud pins would have to be increased to correspond to the thickness of the support plate. Accordingly, a bending load that would be applied from the diaphragm spring to the stud pins would likely result in slanted stud pins. As a result, there is a fear that the desired clutch engagement/disengagement characteristics may not be obtained.